This invention relates to a pressure swing adsorption apparatus for generating oxygen-enriched product gas in which a booster compressor pressurizes the product gas for storage in a plenum and an oxygen sensor monitors the concentration of oxygen in the product gas.
The use of the pressure swing adsorption technique for producing an oxygen-enriched product gas is well known. Pressurized air is sequentially delivered to a plurality of beds of molecular sieve material, and the nitrogen in the air becomes adsorbed by the sieve while the oxygen passes through. The beds are cyclically vented to atmosphere and back flushed with product gas to desorb and discharge the nitrogen from the molecular sieve; and in this fashion, a continuous flow of oxygen-enriched product gas can be generated. Such devices are also known as oxygen concentrators.
In an aircraft environment, an oxygen concentrator may be used to provide product gas to the crew for high altitude flying. In the event of concentrator failure due to loss of electrical power or pressurized air, or a motor or valve failure in the concentrator, a backup oxygen system (BOS) is provided to deliver oxygen for a period of time which will allow the aircraft to descend to an altitude where a supply of breathing oxygen is not required. In such systems, the BOS may be a molecular sieve filled plenum which is charged with product gas by the concentrator. Because of space restrictions in fighter aircraft, the physical size of the BOS is limited; and it may be impossible to store an adequate supply of breathing gas in the BOS at concentrator output pressure to sustain the crew during descent.
For example, an 8 minute supply of breathing gas for a crew of two at a flow rate of 26 liters per minute may be required. If the outlet pressure of the concentrator is in the range of 60 psig, it is impossible to store a sufficient quantity of product gas in the space normally allocated to the BOS. Consequently, a pressure intensifier or booster compressor may be used to increase the pressure of product gas delivered to the BOS so that a reasonably sized storage plenum will be able to contain the required amount of product gas.
Prior art booster compressors have required cycling devices which consist of shuttle valves. The shuttle valve is pneumatically driven and controlled by two pilot valves which are activated by a driver piston. These components are subject to wear and add increased complexity and cost to the concentrator unit.
It is also desirable to provide automatic controls which will fill the BOS plenum with concentrator product gas only when the oxygen content of the product gas is high and will switch the crew member's breathing gas supply from the concentrator output to the BOS when the oxygen content of the concentrator output is low. This requires an oxygen sensor which provides an accurate indication of oxygen concentration and is suitable for use in the temperature and pressure environment of an aircraft.